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Question DetailsAsked on 2/1/2017

Light fixture installation ground wire

Hi if I am installing a simple light fixture after I connect the hot black wires and the neutral white wires is it ok to directly connect the ground wire from the light fixture to the ground wire from the ceiling and bypass connecting either ground wire to the green ground screw on the mounting plate? To my understanding the only time you need to connect the ground wire from the light to this green screw is if there is no ground wire coming from the ceiling. Is that correct?

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3 Answers

0
Votes

All metal components have to be grounded - though different areas have building/electrical code variations on what they allow. Almost all or all require a ground wire from metal fixtures to the circuit ground wire - some allow it through the mounting bracket, some require direct wiring connections. Most require that metal electrical boxes be grounded - some allow that to be via a ground wire connection to a screwed-on mounting bracket, some require a connection direct to the box. So check with your local building code officials after you figure out from the following previous similar questions which method you want to try to use - but unless the circuit ground wire is grounded in the box (if metal) then it should be connected either at the box or on the mounting bracket at a minimum - with a pigtail or by wrapping the solid house circuit wire (not the probably stranded one from the light fixture) around the screw and then to the connection to the fixture wire.

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Answered 1 year ago by LCD

0
Votes

Here is the scientific answer.

If a piece of metal is grounded AND comes in contact with a loose hot wire, then the circut breaker will trip and everybody is safe from shock but in danger of tripping over something in the dark. If the piece of metal is not grounded and comes in contact with a loose hot wire then the circuit breaker will not trip so you will have a non-working light with a charged up mounting plate. This could be dangerous since one would be on a ladder when working on it but hopefully one would turn off the light switch to a dead light fixture before working on it.

However, electric shock and fire are usually the result of several problems at the same time. For example,

1. Mounting plate is not grounded.

2. Hot wire contacts mounting plate.

3. Switch controlling fixture has failed in such a way that the fixture is always on.

Answered 1 year ago by Kestrel Electric

0
Votes

Good summary by Kestrel - where I have heard of people getting zapped most commonly is switch wired wrong (on the neutral rather than hot wire) so the hot wire is always live at the fixture, working in a box where there are multiple leads (like fan and light leads from a multi-function switch) and only one is turned off, or "hot-wiring" an outlet and there is a short to the fixture or mounting bracket AND either the fixture is mounted to the bracket with a plastic decorative center screw mount (some fixtures come that way now) and seats to the wall outside the bracket so it is not grounded there (this requires that it be a 2-wire type fixture without a ground wire, which UL stupidly allows), or that the bracket is not hooked up with the ground wire and is screwed into a non-metallic box.


That is why most jurisdictions require both the ficture ground wire, and that the bracket be grounded. And in many jurisdictions metal boxes also have to be grounded so hopefully mounting screws from fixtures/brackets will serve as a ground path - certainly the safest way to wire it. Some jurisdictions require, and some old-school electricians will only wire, using pigtails - leads from fixture and from circuit ground wire wire-nutted together, with a third "pigtail" leads to the mounting bracket (and leading through the box clamp if metal box) so if the bracket wire somes loose the fixture and box are still grounded. In the old days when all boxes were metal and wiring ran in BX or conduit this was less of a problem, but with plastic fixtures and boxes the risk of accidental electrocution has actually gone up because a loose live wire making contact somewhere does not immediately ground out. Same problem as when UL allowed 2-wire instead of 3-wire power tools and appliances - a fundamental protection went away so manufacturers could save a couple of dimes on cheaper wiring.

Answered 1 year ago by LCD




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